Interesting discussion. When I was growing up on LI (until 2000), we would always sit in the front of the M1 or M3 (leaving Freeport or RVC) and my brother and I would look out the front window. Now you have to get lucky to get an M3 on your train. The last two times that happened while I down visiting, I got to look out the front and the most recent time, someone beat me to the window. Never was asked not to stand there. I'd move if asked by a conductor or engineer.

I remember them having the doors open back in the 90's and you could see them from where you were sitting.

I would think that when the M7 arrived, engineers got used to having more room. Sitting in the cab of an M3 is probably not looked upon with favor. Then having the door closed has got to be unwanted. I don't blame then for not wanting to have someone next to them when they are operating a train.